FODMAPs: Profound Help for Symptoms of IBS

David A. Johnson, MD


September 28, 2012


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Deciphering FODMAPs

Hello. I am Dr. David Johnson, Professor of Medicine and Chief of Gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia. Welcome back to another GI Common Concerns -- Computer Consult.

Today's "curbside consult" is about the FODMAP diet for irritable bowel syndrome (IBS). Let me first define FODMAP. It stands for "fermentable oligosaccharide, disaccharide, monosaccharide, and polyglycans." A diet that excludes these elements may have profound effects on your patients with IBS.

The discovery was made by a group in Australia[1]and has been gaining momentum in the Australian population. FODMAP is now moving into the United States, and slowly people are beginning to understand the importance of it. The intake of certain dietary sugars plays a role not only in fermentation and osmotic effects in the bowel but also in afferent visceral sensitivities. The effects of these foods can be profound.


With FODMAP, we are primarily talking about carbohydrates. Let me just run through what carbohydrates are and what they can do, starting with lactose.

Lactose is a disaccharide that is very common in milk products. Up to 90% of people have some degree of lactose intolerance, a rate that increases on the basis of ethnicity. Lactose intolerance is more common in blacks, Indians, and Hispanics. There may be a relative tolerance to lactose in Europeans, but this tolerance tends to be lost with age.

Certain things will change a person's tolerance to lactose, because it requires lactase, a small bowel enzyme located on the villi, for digestion. If a person has gastroenteritis or if someone with Crohn disease experiences a small bowel flare, this may produce transient lactose intolerance. Remember this when you are counseling patients who are experiencing increasing diarrhea in association with their underlying disease.

Lactose intolerance is the inability to tolerate lactose in foods. One food that you need to be aware of that is relatively free of lactose is hard cheese, because the whey is typically taken off as these hard cheeses develop. They [hard cheeses] have a very low lactose component, along with sour cream and butter. These foods are allowed on a FODMAP diet.

The enzyme lactase, such as in Lactaid, is added to certain food products to make people more tolerant to lactose. Yogurt, because of the lactobacillus, may also be tolerated. However, frozen yogurt is not on the list. Patients may need to test the water with yogurt.

What I hear from patients is, "No, I'm not milk intolerant." But lo and behold, they have good days and bad days. If you go back and look at the relative proportion of milk intake that day and then add in the other FODMAP-type foods, you might see that milk is contributing to the symptoms. So, when we start to talk about FODMAP exclusions, there may be foods that people discover that they don't have to exclude entirely; however, they may choose to minimize these foods or add products such as Lactaid to their diets.


Fructose is a monosaccharide. The monosaccharides are glucose, fructose, and galactose. Fructose and glucose combine to form sucrose, which is standard table sugar.

Fructose is a sugar that we see in honey and in a lot of fruits, such as pears, apples, grapes, raisins, prunes, peaches, and pineapples. These fruits are very high in fructose.

The fructose balance of food is what drives the absorption of fructose. When the fructose component exceeds the sucrose component in foods containing both, there is an intolerance of fructose. These fructose-rich foods may warrant elimination from the diet.


Fructans are oligosaccharides, polymers of fructose molecules, found in wheat and many types of vegetables (eg, asparagus, artichokes, onions). Longer-chain fructans are called inulins. Inulins are sometimes added as soluble fiber to yogurt. However, some yogurts can actually work against you. If a patient who eats a lot of yogurt is having a lot of gas or diarrhea, the yogurt could actually be exacerbating their symptoms.

Fructans may also be found in a variety of sugar-laden fruits, such as pears, pineapples, bananas, prunes, and apples. I always wondered why the BRAT [bananas, rice, applesauce, toast] diet included apples as a component to reduce diarrhea. Apples are a fructose-rich food. I always tell people to avoid apples when they have diarrhea.

Wheat is the most common source of fructans, accounting for about 70% of fructan intake in the United States. If you test patients for celiac disease and they come back as celiac negative and TTG negative, with no serologic evidence of wheat intolerance, you start to look at wheat or gluten exclusion in some of these patients. You will find that they have remarkable success and symptom improvement, and it may be because of the fructans in wheat. This gets back to the idea of good days and bad days. A patient may consume more of the fructan-containing wheat and have a bad day. This may be related to the relative balance of the other FODMAP components that they ingested during this time.


Galactan is a polymer of galactose. Humans lack a digestive enzyme necessary to break down and absorb galactans.

Galactans are found in certain vegetables, such as legumes, soybeans, peas, wax beans, and baked beans. The inability to digest galactans has given beans the nickname "musical fruit" because they contain stachyose and raffinose. Without enzymes to digest these oligosaccharides, galactans are poorly digested. They create not only an osmotic effect, but as a fermentable sugar in the colon, they also create gas, and there may be afferent sensory changes as well.


The last component of FODMAP is the polyols, the sugar alcohols. Where these polyols really make a difference is in sorbitol, which is a natural component of certain fruits, such as apples, prunes, and particularly watermelon.

Look closely at what foods your patients may be eating that contain polyols because these substances are frequently used as dietetic sweeteners. Certain food additives will have hydrogenated polyols. You need to make sure, for the FODMAP diet, that patients become good label readers and start to look at these hydrogenated polyols that may be components of sweeteners. Corn syrup is a fructose-rich component frequently added to foods as well.

Polyols (mannitol, sorbitol, and xylitol) are in many dietetic foods, candies, and gum as sweeteners. Polyols can make a big difference when you start to do a component analysis of the FODMAP diet.

Improving Care for IBS

We have a lot to learn about how to counsel our patients who have IBS. The answer is not just "eat more fiber." It is to understand the components of the diet. Individuals are just that -- individuals. There may be certain foods that people are particularly sensitive to.

There is a wonderful book, called IBS--Free at Last! A Revolutionary, New Step-by-Step Method for Those Who Have Tried Everything: Control IBS Symptoms by Limiting FODMAPs Carbohydrates in Your Diet by a dietician named Patsy Catsos.[2] I recommend this book to my patients. It is a comprehensive evaluation of FODMAPs and goes straight to an elimination or challenge diet.

Speaking as someone who is not truly an expert in IBS, this has made a profound impact on my expertise and ability to provide meaningful care to my patients with IBS. Think about it also for your patients with inflammatory bowel disease as they start to flare. These small things can make a very meaningful difference. You need to learn more about this. I hope this has helped you for the next time you counsel a patient with gas, constipation, bloating, or diarrhea. These problems are very frequent in our population, and we can make a profound difference by doing a better job.

I am Dr. David Johnson. Thanks again for listening.